Skepticism is primarily concerned with questioning the reliability and validity of our knowledge, exploring the limits of what we can know and how we can know it.

Pyrrho of Elis, a Greek philosopher who lived in the 3rd century BCE, is widely regarded as the founder of skepticism. He argued that all knowledge is uncertain and that we should suspend judgment on all matters.

Pyrrhonian skepticism is based on the argument from ignorance, which states that we cannot know anything for certain because our senses are unreliable and our reason is fallible. Therefore, we should withhold judgment on all matters.

Academic skepticism, as propounded by philosophers like Carneades and Arcesilaus, emphasizes the practice of withholding judgment (epochē) on all matters. They argued that since we cannot attain certain knowledge, we should refrain from making any definitive claims.

The argument from regress, also known as the problem of induction, is a skeptical argument that challenges the reliability of inductive reasoning. It points out that our beliefs about the world are based on past experiences, but there is no guarantee that these experiences will continue to hold true in the future.

In his skeptical meditations, Descartes sought to question the reliability of reason itself. He argued that our senses can deceive us and that our memories are fallible. Therefore, he doubted the validity of all knowledge derived from these sources.

The argument from relativism highlights the influence of culture and language on our knowledge. It suggests that what we consider to be true or justified is relative to our cultural and linguistic context, rather than being universally valid.

One objection to the skeptical argument from illusion is that our experiences, despite being potentially deceptive, exhibit a degree of coherence and consistency. This coherence suggests that there is an underlying reality that is independent of our subjective perceptions.

The argument from moral relativism questions the existence of objective moral values. It points out that moral beliefs and practices vary across cultures and historical periods, suggesting that morality is subjective and relative to specific contexts.

The argument from intersubjectivity counters the skeptical challenge of solipsism by emphasizing the shared experiences and agreements among different individuals. It suggests that the existence of a common reality is supported by the fact that multiple observers can perceive and interact with the same objects and events.

The argument from circularity, also known as the Münchhausen trilemma, points out the problem of infinite regress in justification. It argues that if we attempt to justify our beliefs by appealing to other beliefs, we either end up in an infinite chain of justifications or we eventually reach a point where our beliefs are justified without any further justification, which is problematic.

Fideism, as a response to skepticism, emphasizes the role of faith and revelation in acquiring knowledge and overcoming skeptical doubts. It argues that certain truths can be known through faith, even if they cannot be proven through reason or empirical evidence.

The argument from fallibility of memory highlights the unreliability of memory as a source of knowledge. It points out that memories can be distorted, forgotten, or manipulated, casting doubt on the accuracy and trustworthiness of our recollections.

Epistemological skepticism is primarily concerned with questioning the limits of human knowledge and the reliability of our cognitive faculties. It explores the extent to which we can know things and how we can justify our beliefs.

The argument from dreaming points out the difficulty in distinguishing between dreams and reality. It suggests that our experiences in dreams can be so vivid and realistic that it becomes challenging to determine whether we are awake or asleep, raising doubts about the reliability of our sensory perceptions.